BMW 70’s Era Tire sizes and their equivalents

I’m posting this so I have my own record of it. I always have to look it up and this is a great place to store my ‘notes’.

Typically, tire sizes for a R75/5 R90/6 R90s R100S, etc will have a:

3.25 x 19 Front
4.00 x 18 Rear

The metric metric equivalents would be 90/90-19 for the front and 100/90-18 or possibly 110/90-18 for the rear.

Final drive spline rehab

I can’t remember the condition of this final drive when I assembled my 77 R100s back in 2003.  When I had my rear tire replaced recently, I noticed how terrible the splines are. The splines on the wheel are better then the final drive but they will need replacing someday too.

I found this drive with the same ratio and cleaned it up and replaced the spline.  Now it is time to swap the drives.

While it is apart, I am taking the opportunity to pull the tranny back and lube the clutch splines as well.

Bmw final drive spline

Bmw R100S final drive spline replacement

Airhead center stand rehab

Anybody who has ever owned an airhead from the 70s has most likely come across a broken center stand tab. The problem is that after the stand gets kicked down, most people put their foot on the tab, and not on the center stand when they lift the bike up on the stand. And, over time, the thin kick tab, and the weak weld eventually gives out.
Most people have fixed it by welding part of a nail back in the same area as the original kick tab.
I think this is one of those things BMW could have made better… so i improved upon the original design.

Click the photos for larger versions.

Here is a photo of an original center stand (taken of my 1977 R100s):

Of course, i didn’t take any photos of this particular center stand before i started the project…. dough!

Center Stand repair job:

Clean up:

****EDIT This new tab might interfere with your stock side stand. I do not use a side stand on my cafe bikes so I can’t say for sure.

Broken clutch cable – repair on the road

The other day i had to work on location about 35 miles from my home (typically i work 2 miles away from home).  In order to beat the insane traffic at that hour, i loaded up the saddle bags on my ’77 R100s and beat the 2 hour stop and go car traffic by 1.25 hours. Lane Splitting in California is awesome.
After a hard day’s work in the hot and windy ‘central valley’ i got in my bike to shoot home. While at the stop sign about to pull into traffic i pull the clutch to get in first gear and then.. SNAP!  Broken Clutch Cable. 35 miles from home. If you need truck repair parts, check
I immediately shut the bike off and pushed it to the side of the road.
Luckily i have a fairly complete tool kit hiding under the seat chock full of basic wrenches, sockets, tape, rags, etc…
I took photos after i view publisher site for details and started to take everything apart and replaced it with a NEW BMW Clutch cable. The previous clutch cable wasn’t BMW. Motobins in the UK sold it to me and from the day i got it, i was suspicious and contacted them about it.  They assured me it was better then BMW’s… i think after 20,000 miles, a BMW cable would still function.  Motobins sold me some crappy pipes about 8 years ago too.  I’m NEVER using them again for motorcycle parts.
Here is my roadside repair:

It seems the very end of the clutch cable’s ‘catch’ piece gave out. That separate piece should be at the very end of the cable. Then the entire cable’s end fits inside the large round cylinder.

With no other option, i had to think of a solution or wait hours to get home via tow truck or friend with a pickup. I managed to wedge the broken piece of the cable into the Cylinder aka ‘nipple holder’. And yes, that is what BMW calls it.

The cable’s end is usually contained inside the cylinder but since the end was broken off, i had to think of something else. I ended up wedging the cylinder as far into the handle as i could. This meant that i lost about a half an inch of Clutch Cable length.  It took some effort trying to get the other end of the cable to connect to the clutch arm. 

Clutch Handle back in place with wedged cylinder and cable end sticking half way out.

Luckily i have a roll of electrical tape in my tool kit. I was able to tightly wrap around the cable’s end and the clutch handle. Phew. Temporary fix.

Funny thing happened on the freeway on the way home.  I was lane splitting through 15mph traffic on the freeway and recognized a classic ’59 teal Chevy pick-up truck.  It happened to be a great friend of mine.  I pulled along side and told him the story (while riding down the freeway). He said he’d throw the bike in the back. Talk about luck! But i decided to press my luck and I declined the offer… only to have the clutch cable’s cylinder fall out of the handle after we split ways.  I called him up and we went to my house to get a ramp and straps… but by that time he got there, i did the repair again and this time i wrapped the electrical tape even tighter and it was enough to get me home.
No more non-‘BMW’ parts unless they are a proven upgrade!